4.3. Preparing Files for TFTP Net Booting

If your machine is connected to a local area network, you may be able
to boot it over the network from another machine, using TFTP. If you
intend to boot the installation system from another machine, the
boot files will need to be placed in specific locations on that machine,
and the machine configured to support booting of your specific machine.

You need to set up a TFTP server, and for many machines a DHCP
server, or RARP
server, or BOOTP
server.

The Reverse Address Resolution Protocol (RARP) is
one way to tell your client what IP address to use for itself. Another
way is to use the BOOTP protocol.BOOTP is an IP protocol that
informs a computer of its IP address and where on the network to obtain
a boot image.
The DHCP (Dynamic Host Configuration Protocol) is a more flexible,
backwards-compatible extension of BOOTP.
Some systems can only be configured via DHCP.

The Trivial File Transfer Protocol (TFTP) is used to serve the boot
image to the client. Theoretically, any server, on any platform,
which implements these protocols, may be used. In the examples in
this section, we shall provide commands for SunOS 4.x, SunOS 5.x
(a.k.a. Solaris), and GNU/Linux.

4.3.1. Setting up RARP server

To set up RARP, you need to know the Ethernet address (a.k.a. the MAC address)
of the client computers to be installed.
If you don't know this information, you can
pick it off the initial OpenPROM boot messages, use the
OpenBoot .enet-addr command, or
boot into “Rescue” mode (e.g., from the rescue floppy) and use the
command ip addr show dev eth0.

On a RARP server system using a Linux 2.4 or 2.6 kernel, or Solaris/SunOS,
you use the rarpd program.
You need to ensure that the Ethernet hardware address for the client is
listed in the “ethers” database (either in the
/etc/ethers file, or via NIS/NIS+) and in the
“hosts” database. Then you need to start the RARP daemon.
Issue the command (as root): /usr/sbin/rarpd -a
on most Linux systems and SunOS 5 (Solaris 2),
/usr/sbin/in.rarpd -a on some other Linux systems,
or /usr/etc/rarpd -a in SunOS 4 (Solaris 1).

4.3.2. Setting up a DHCP server

One free software DHCP server is ISC dhcpd.
For Debian GNU/Linux, the dhcp3-server package is
recommended. Here is a sample configuration file for it (see
/etc/dhcp3/dhcpd.conf):

In this example, there is one server
servername which performs all of the work
of DHCP server, TFTP server, and network gateway. You will almost
certainly need to change the domain-name options, as well as the
server name and client hardware address. The
filename option should be the name of the
file which will be retrieved via TFTP.

After you have edited the dhcpd configuration file,
restart it with /etc/init.d/dhcp3-server restart.

4.3.3. Setting up a BOOTP server

There are two BOOTP servers available for GNU/Linux. The first is CMU
bootpd. The other is actually a DHCP server: ISC
dhcpd. In Debian GNU/Linux these are contained in the
bootp and dhcp3-server
packages respectively.

To use CMU bootpd, you must first uncomment (or
add) the relevant line in /etc/inetd.conf. On
Debian GNU/Linux, you can run update-inetd --enable
bootps, then /etc/init.d/inetd
reload to do so. Just in case your BOOTP server does not
run Debian, the line in question should look like:

bootps dgram udp wait root /usr/sbin/bootpd bootpd -i -t 120

Now, you must create an /etc/bootptab file. This
has the same sort of familiar and cryptic format as the good old BSD
printcap, termcap, and
disktab files. See the
bootptab manual page for more information. For
CMU bootpd, you will need to know the hardware
(MAC) address of the client. Here is an example
/etc/bootptab:

You will need to change at least the “ha” option, which
specifies the hardware address of the client. The “bf”
option specifies the file a client should retrieve via TFTP; see
Section 4.3.5, “Move TFTP Images Into Place” for more details.

By contrast, setting up BOOTP with ISC dhcpd is
really easy, because it treats BOOTP clients as a moderately special
case of DHCP clients. Some architectures require a complex
configuration for booting clients via BOOTP. If yours is one of
those, read the section Section 4.3.2, “Setting up a DHCP server”. Otherwise you
will probably be able to get away with simply adding the
allow bootp directive to the configuration
block for the subnet containing the client in
/etc/dhcp3/dhcpd.conf, and restart
dhcpd with /etc/init.d/dhcp3-server
restart.

4.3.4. Enabling the TFTP Server

To get the TFTP server ready to go, you should first make sure that
tftpd is enabled.

In the case of tftpd-hpa there are two ways the
service can be run. It can be started on demand by the system's
inetd daemon, or it can be set up to run as an
independent daemon. Which of these methods is used is selected when the
package is installed and can be changed by reconfiguring the package.

Note

Historically, TFTP servers used /tftpboot as directory
to serve images from. However, Debian GNU/Linux packages may use other directories
to comply with the Filesystem Hierarchy
Standard. For example, tftpd-hpa by default
uses /srv/tftp. You may have to adjust the
configuration examples in this section accordingly.

All in.tftpd alternatives available in Debian should
log TFTP requests to the system logs by default. Some of them support a
-v argument to increase verbosity.
It is recommended to check these log messages in case of boot problems
as they are a good starting point for diagnosing the cause of errors.

4.3.5. Move TFTP Images Into Place

Next, place the TFTP boot image you need, as found in
Section 4.2.1, “Where to Find Installation Images”, in the tftpd
boot image directory. You may have to make a link from that
file to the file which tftpd will use for booting a
particular client. Unfortunately, the file name is determined by the
TFTP client, and there are no strong standards.

4.3.5.1. SPARC TFTP Booting

Some SPARC architectures add the subarchitecture names, such as
“SUN4M” or “SUN4C”, to the filename. Thus,
if your system's subarchitecture is a SUN4C, and its IP is 192.168.1.3,
the filename would be C0A80103.SUN4C. However,
there are also subarchitectures where the file the client looks for is
just client-ip-in-hex. An easy way to determine the
hexadecimal code for the IP address is to enter the following command
in a shell (assuming the machine's intended IP is 10.0.0.4).

$ printf '%.2x%.2x%.2x%.2x\n' 10 0 0 4

To get to the correct filename, you will need to change all letters to
uppercase and if necessary append the subarchitecture name.

If you've done all this correctly, giving the command boot
net from the OpenPROM should load the image. If the image
cannot be found, try checking the logs on your tftp server to see which
image name is being requested.

You can also force some sparc systems to look for a specific file name
by adding it to the end of the OpenPROM boot command, such as
boot net my-sparc.image. This must still reside
in the directory that the TFTP server looks in.